docs: def _write_fact(self, fact_tuple):
          """
          Create new fact element and populate attributes.
  
          Once the child is prepared append it to ``fact_list``.
          """
          fact = self.document.createElement("fact")
          fact.setAttribute('start', fact_tuple.start)
          fact.setAttribute('end', fact_tuple.end)
          fact.setAttribute('activity', fact_tuple.activity)
          fact.setAttribute('duration', fact_tuple.duration)
          fact.setAttribute('category', fact_tuple.category)
          fact.setAttribute('description', fact_tuple.description)
          self.fact_list.appendChild(fact)